Classifications

• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/29—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the position or the direction of light beams, i.e. deflection
  • G02F1/31—Digital deflection, i.e. optical switching
  • G02F1/313—Digital deflection, i.e. optical switching in an optical waveguide structure
  • G02F1/3132—Digital deflection, i.e. optical switching in an optical waveguide structure of directional coupler type
• • G—PHYSICS
  • G02—OPTICS
  • G02B—OPTICAL ELEMENTS, SYSTEMS OR APPARATUS
  • G02B6/00—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings
  • G02B6/10—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type
  • G02B6/12—Light guides; Structural details of arrangements comprising light guides and other optical elements, e.g. couplings of the optical waveguide type of the integrated circuit kind
  • G02B2006/12083—Constructional arrangements
  • G02B2006/12107—Grating
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F1/00—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics
  • G02F1/01—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour 
  • G02F1/0147—Devices or arrangements for the control of the intensity, colour, phase, polarisation or direction of light arriving from an independent light source, e.g. switching, gating or modulating; Non-linear optics for the control of the intensity, phase, polarisation or colour  based on thermo-optic effects
• • G—PHYSICS
  • G02—OPTICS
  • G02F—OPTICAL DEVICES OR ARRANGEMENTS FOR THE CONTROL OF LIGHT BY MODIFICATION OF THE OPTICAL PROPERTIES OF THE MEDIA OF THE ELEMENTS INVOLVED THEREIN; NON-LINEAR OPTICS; FREQUENCY-CHANGING OF LIGHT; OPTICAL LOGIC ELEMENTS; OPTICAL ANALOGUE/DIGITAL CONVERTERS
  • G02F2201/00—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00
  • G02F2201/30—Constructional arrangements not provided for in groups G02F1/00 - G02F7/00 grating
  • G02F2201/307—Reflective grating, i.e. Bragg grating

Definitions

• the invention relates to a tuneable grating assisted directional optical coupler, which couples a predetermined wavelength among the channels of an input signal between two waveguides using a grating provided in the coupling region thereof. More particularly the coupler of the present invention is wavelength tuneable, i.e. the predetermined wavelength can be changed from one targeted wavelength to another. Technological background Optical devices for optical channel filtering, such as wavelength add/drop filters, bandpass filters, directional couplers, etc, are important elements of optical telecommunication systems.
• Wavelength Division Multiplexing a plurality of N mutually independent optical signals are transmitted along a line.
• Each of these independent signals has a respective transmission wavelengths ⁇ , ⁇ 2 ..., ⁇ N , which are different from each other and each of which defines a transmission "channel". All these wavelengths, which have a spacing between them, should be included in a useful amplification bandwidth of optical amplifiers used in the line.
• it must be possible to wavelength selectively drop the optical signal coming in through an optical fiber (or through another optical conduit) to a fiber/conduit conveying to the respective user/destination and to wavelength selectively add signals to the fiber.
• couplers including a grating which is a periodic structure formed by spatially varying refractive index distribution throughout a defined volume or the boundary of a guiding region.
• a periodic perturbation (grating) inserted in the coupling region such that its wave-vector obeys to one of the following relationships
• A is the grating periodicity
• ⁇ i and ⁇ 2 are the propagation constant in waveguides 1 and 2 at ⁇ 0 , there is coupling between the two waveguides only at the specific wavelength ⁇ 0 named above. If Eq. (I) is satisfied, then the wavelength ⁇ o is coupled in the backward direction from one waveguide to the other and the directional coupler is said to be a contra-directional coupler, whereas if Eq. (II) is satisfied, the wavelength ⁇ 0 is coupled in the forward direction and the coupler is said to be a co-directional coupler.
• a particularly desiderable additional characteristic of optical couplers is wavelength tunability, so that the dropped wavelength may be changed, in order to increase the flexibility of networks.
• the goal of a tuneable coupler is therefore to select one channel (or several channels) in a given incoming input optical signal and transmitting all other channels through the filter, said channel being changeable.
• tuneable optical filters have been developed.
• a proposed solution has been to realize the core region of one of the two waveguides in a tuneable material, i.e. a material whose refractive index may be changed, therefore changing ni or n 2 . This implies, a change in the filtered wavelength ⁇ 0 (see eq. (III)).
• °C will typically shift the filter wavelength by less than 1 nm. This may restrict the applications where the desiderable tuning range is of several nm.
• a tuneable add/drop multiplexer having a grating printed in a single- mode polymeric waveguide with a thin-film heater is described.
• OADM Optical Add/Drop Multiplexer
• the high cost of the circulators makes the device too expensive.
• v Polarisation insensitive and tuneable optical add and drop multiplexer utising vertically stacked buried semiconductor waveguides published in Electronics Letters vol. 35, No. 20, p. 1733-1734
• a tuneable, vertical and contra-directional coupler filter in which specially designed buried semiconductor waveguides are used, is disclosed.
• the two waveguides are made of InGaAsP, are buried in a InP cladding and a grating is formed between the waveguides in the filter region. The tunability is achieved by changing the temperature.
• III-V semiconductors such as InGaAsP should be varied of at least 500 °C, which implies a huge thermal variation of the overall device, which can be detrimental for the device performances. They have further observed that fabrication technology based on III-V semiconductors is rather complex and expensive.
• Hybrid silica-polymer structure for integrated optical waveguides with new potentialities published in Material Science and Engineering vol. B57, p. 155- 160, a coupler comprising two coplanar waveguides having silica cores and a polymer cladding is described.
• the directional coupler of this paper comprises two ridge cores made of silica which are covered by the same polymer cladding.
• a Bragg grating is UV-induced in both waveguides in the central part of each sample.
• the negative thermal optical coefficient for the polymer refractive index enables the authors to auto-stabilise the Bragg grating in temperature.
• US patent n. 6097865 to Alferness et al. discloses a wavelength filter having a low index waveguide, a high index waveguide, having substantially different geometries which results in substantially different effective indices, and a grating for coupling therebetween. Both waveguides are made of InGaAsP. In this patent, the so obtained high effective index differential of the filter waveguides is desired in order to achieve a high bandwidth and reduce cross-talk. Summary of the invention The present invention relates to a grating assisted directional optical coupler, in particular to a tuneable asynchronous coupler, i.e. a directional coupler such that the two waveguides have different effective refractive indices so that no coupling normally occurs between them.
• Each of the waveguides comprises a core and a cladding.
• the directional coupler comprises a coupling region, where the two waveguide cores are in close proximity to each other so that coupling is made possible, and two input/output regions where the two waveguide cores are separated by a distance that is large enough to avoid coupling between the two waveguides.
• the optical signal enters or exits to or from the input/output regions.
• the two waveguide cores are placed in two different vertically stacked horizontal planes, i.e., the cores are vertically stacked and separated by a vertical distance d. In this case, the horizontal distance between the two waveguide cores in the input/output regions decreases in the coupling region to a value small enough to allow coupling.
• a periodic perturbation preferably a Bragg grating, is placed in the coupling region and it is designed to induce either a co-directional or a contra- directional coupling between the two waveguides.
• ⁇ ni and ⁇ n 2 are the variations of the effective indices of the first and the second waveguide, respectively.
• n tot is the algebraic sum of the effective indices of the two
• the An value of — of the tuneable material where ⁇ n is the variation of the n refractive index n for said variation of the external parameter, should be considered.
• ⁇ T not larger than 200°C
• — should be not smaller than 2xl0 "2 , n
• Temperature variations not larger than 100 °C are preferred to improve the stability of the employed polymers. More generally, temperature variations not larger than 100 °C are preferred because functioning of the optical device, i.e., the coupler, can be attained with relatively low power consumption.
• thermo-optic coefficient 10 ⁇ 7 °C
• n is their refractive index and T the temperature, in particular polymers, can be employed.
• thermo-optic materials materials having electro-optical properties as long as their refractive index can be varied in a relatively wide range, as liquid crystals, for a reasonable variation of the applied electric field.
• the parameter of interest is the electro-optic coefficient r of the material; r is correlated to the
• Materials of interest are those having an electro-optic coefficient
• a class of materials that may have these properties is that comprising liquid crystal materials.
• electro-optic materials are possible tuneable materials according to the invention, in particular in a technology based on silicon-compounds materials, employment of polymers is preferred to that of liquid crystals because in the latter case technology can be more complex as confinement materials are necessary to confine the liquid crystal.
• the employment of electro-optic materials generally requires two electrodes for the tuning of the electric field of the tuneable material. This may increase complexity of the tuneable device when compared to the employment of thermo-optic materials.
• a tuneable coupler which is based on a realisation of a waveguide and a core using standard techniques and standard materials, on which the tuneable cladding is deposited.
• a first silicon compounds-based waveguide comprising a first core and a first cladding is realised on a substrate and on top of the first silica-based waveguide a second silica-based core is fabricated.
• a tuneable polymer cladding is then deposited onto the second core. This allows to avoid any rather complex polymer etching or troubles of connections between polymer and silica. This embodiment of the invention allows therefore to combine the good thermo-optical properties of polymers and the quality of the silicon-compounds based waveguides without giving rise to complex fabrication steps.
• silicon compounds we refer to materials comprising substantially silica glass, i.e., SiO 2 , ternary compounds such as SiO x N y or Si 3 N 4 and its non- stochiometric compounds.
• Dopants such as Ge, B, P or Al, can be intended to be comprised in the matrix of silicon compounds, for instance in order to modify the refractive index of the material.
• FIG. 1 is a schematic cross-sectional view of a tuneable grating assisted directional optical coupler according to the present invention
• FIG. 2a schematically depicts a lateral cross-sectional-view of a contra- directional grating assisted directional optical coupler of fig. 1
• FIG. 2b schematically depicts a co-directional grating assisted directional optical coupler of fig. 1
• FIG. 3 is a graph showing the spectra response of the contra-directional grating assisted directional optical coupler of the type shown in fig.
• FIG. 4 is a cross sectional view of a second embodiment of the contra- directional grating assisted directional optical coupler of the type shown in fig. 2a;
• FIG. 5 is a cross sectional view of the co-directional grating assisted directional optical coupler of the type shown in fig. 2b;
• - FIG. 6 is an enlarged cross-sectional view of a detail of the co- directional grating assisted directional optical coupler of fig. 5;
• FIG. 7 is a graph showing the response (normalized power) of the co- directional coupler of figs. 5 and 6; - FIG.
• FIG. 8 shows a schematic wave-vector diagram including the wave- vector ( ⁇ ) positions corresponding to the C-band in the two waveguides forming the coupler of fig. 1; - FIG. 9 is a graph showing the filter spectrum of an additional embodiment of the coupler of fig. 1; - FIG. 10 is a graph showing the filter spectrum of an additional embodiment of the coupler of fig. 1; - FIG. 11 schematically depicts an add/drop optical device including at plurality of tuneable grating assisted directional optical coupler of fig. 1.
• 10 indicates a tuneable grating assisted directional optical coupler according to the present invention.
• Figure 1 schematically illustrates a cross-sectional view of a coupler 10 comprising a first 1 and a second waveguide 2, in close proximity with each other so as to define a coupling region of length L (taken along the direction of mode propagation) and form a directional coupler.
• First waveguide 1 comprises a first core 7 and a first cladding 4 and second waveguide 2 comprises a second core 8 and second cladding 3.
• the refractive index n ⁇ c of the first core should be larger than the refractive index n 4 of the first cladding and the refractive index n 2c of the second core is larger than the refractive index n 3 of the second cladding.
• the waveguides 1,2 are realised on a substrate 6, preferably a silicon wafer, and have effective refractive indices ni and n 2 , respectively, different from each other.
• the coupler 10 is therefore asynchronous and, depending on the difference n ⁇ -n 2 and the distance d between the two waveguide cores 7,8, the amount of optical power exchange between the two waveguides may be reduced to very low values ( ⁇ 1%): no coupling occurs between the two waveguides in the absence of a grating.
• the refractive index difference between the two waveguides 1,2 is achieved using different materials or using substantially different geometries to realize the two waveguides.
• the first and second waveguide 1,2 each comprises an input port la, 2a and an output port lb, 2b.
• the coupler 10 receives at the input port la of the first waveguide 1, upstream of the coupling region, an input optical, signal 11 which includes at least a signal wavelength ⁇ 0 .
• the optical signal 11 carries a number of optical channels ⁇ i, , ⁇ N , more preferably comprised between about 1530 nm and 1565 nm, which corresponds approximately to the C-band.
• the input signal 11 can be a DWDM signal with 100 or 50 GHz of channel spacing.
• a periodic perturbation 12 preferably a periodic perturbation (having period ⁇ ) of the refractive index, is induced in the coupling region L of the coupler 10 either of the first waveguide 1 or of the second waveguide 2 by any appropriate technique.
• the periodic perturbation is introduced in the second waveguide 2.
• the periodic perturbation 12 preferably defines a linear Bragg grating, however it may also be embodied by a non linear perturbation grating as a chirped or apodised grating.
• Various arrangements for the position of the periodic perturbation 12 are conceivable, with the constraint that the optical fields of the input and the output waveguide 1,2 overlap in at least a portion of the periodic perturbation 12.
• Gratings can be produced by a variety of techniques such as UV-induced photolithography, etching or electron beam writing, said techniques can be chosen also in dependence of the desired characteristics of the grating.
• the wave-vector K of the grating 12 obeys either to eq. (I) or to eq. (II).
• the K-vector of the grating 12 compensates for the ⁇ -mismatch between the two waveguides 1,2 thus restoring synchronism and complete power exchange at ⁇ 0 : this wavelength is coupled from a waveguide to the other.
• this process is determined by the strength of the grating and the distance d between the two waveguide cores 7,8 and may be tailored to a specific value by varying these two parameters.
• the coupler 10 is defined as "contra-directional" and the input optical signal 11 launched in the input port la passes unaffected through input waveguide 1 except for the channel of wavelength ⁇ 0 which is coupled in the backward
• the forward direction from the input waveguide 1 into the output waveguide 2 and the coupler 10 is called a "co-directional coupler", represented in fig. 2b, where the periodic perturbation 12 is realized on the second waveguide 2.
• the periodic perturbation 12 is preferably placed in the output waveguide 2, as shown in the embodiments of Figs. 2a and 2b, in order to reduce optical losses of the transmitted signal (at wavelengths different than those coupled back or forward) due to the grating, it is to be understood that a coupler in which the periodic perturbation is introduced in the input waveguide, e.g., waveguide 1, is also conceivable. Referring back to Fig.
• waveguide cores 7, 8 is preferably fabricated from silicon compounds-based material, which may also include dopants such as Ge, B, P, or Al.
• the core of the input waveguide is made of silica with the possible addition of one or more dopants. It is understood that other materials may be employed as known by those skilled in the art. Consequently, an exhaustive list of possible materials used to create these components is not offered herein.
• the first waveguide 1 comprises a first cladding 4 surrounding the first core 7, said cladding being fabricated preferably from a "non-tuneable" (whose meaning will be explained below) material, even more preferably from a silicon compounds-based material, more preferably from undoped or doped SiO 2 .
• the first cladding 4 may completely surround the first core 7, as represented in fig. 1, or it may be possible, for example, that the first core 7 is in contact with the substrate 6 for a portion of its boundary and for the remaining portion is in contact with the first cladding 4. It is however to be understood that the material surrounding the first core should always have a refractive index which is lower than that of the core to ensure the propagation of guided modes.
• the second waveguide 2 comprises a second cladding 3 which is realized in a tuneable material, surrounding (in one of the possible different ways above described for the first core) the second core 8.
• tuneable material we refer to a material whose refractive index can be varied by changing an external parameter, such as the temperature or the electric field.
• the cladding material of the present invention is taken from the category of materials classified as polymers, which have an index of refraction n that varies with temperature T, dn n 3 (T). In particular their preferred is not smaller than lxlO ⁇ 4 /°C, which dT
• Preferred polymers are DeSoliteTM 3471- 1-129 produced by DSM or SylgardTM 184 produced by Dow Corning. However any transparent polymer satisfying the above written requirements is suitable for the realization of the cladding 3.
• the suitable polymer for the waveguide cladding should be selected so that its refractive index n 3 (T) remains smaller than that of the waveguide core in the entire temperature range of interest for the functioning and tunability of the device.
• silica has a refractive index that varies with temperature, the order of magnitude of its thermo-optic coefficient is sensibly smaller than those of polymers, namely at least a factor of 10, the thermo- optic coefficient of silica being of about 10 "5 /°C Considering its refractive An index of 1.45 (for undoped silica), the value of — for a variation of 200°C is n only of the order of 10 "3 . Therefore, within this context, silica is considered a
• non-tuneable material With the term “non-tuneable material”, we refer to
• non-tuneable materials comprise also materials having relatively high thermo-optic or
• thermo-optic coefficient but low , i.e., lower than 10 "2 for a temperature n variation of 100°C or for an electric field variation of 1 V/ ⁇ m.
• a variation in temperature of 100 °C gives a variation in the refractive index ⁇ n of 0.025,
• the periodic perturbation is realised on the core of the non-tuneable waveguide, in particular in case of a contra-directional coupler.
• the grating is generally a so-called "strong grating", in which the variation of refraction index along the grating is larger than about 10 "3 .
• the depth of the etched areas of the grating should be relatively deep in order to have a strong grating. This can make the realisation of a polymeric cladding over the grating cumbersome, as the polymeric material may not completely fill the deep regions of the grating leaving unfilled portions, in which case the response of the coupler would not be optimal.
• this technological difficulty can be reduced in case of a "weak" grating, in which the refractive index variation is smaller than about 10 "3 (a shallow etching or another non-etching technique can be used for the grating) so that the grating can be alternatively placed either in the tuneable waveguide or in the non-tuneable one.
• the grating is induced in the core of either of the waveguides.
• configurations comprising a grating in one of the cladding layers can be envisaged.
• the grating is realised on the output waveguide to minimise losses.
• the coupler of the present invention is always depicted as a "vertical" coupler, i.e. a coupler wherein the waveguides 1,2 are vertically stacked, the teachings of the present invention apply to a coupler having coplanar waveguides as well. Additionally, although the two waveguides 1,2 are shown having a square or rectangular cross-section (both of the cores and claddings), waveguides with a differently shaped cross-section may be used.
• a contra-directional coupler 10 including two vertically stacked waveguides 1,2 on a substrate 6 is shown.
• the input waveguide in whose core also the grating is formed is the lower waveguide 1.
• the filtered wavelength is transferred to the upper waveguide 2.
• the core of the input waveguide 7 is square, its dimensions are l.lxl.l ⁇ m 2 and it is realised in SiO x ⁇ y ⁇ having a refractive index n ic of 1.7, while the core 8 of the output waveguide 2 is also square (l.lxl.l ⁇ m 2 as above) and it is realised in SiO x2 N y2 having a refractive index n 2c of 1.567.
• the distance d between the two cores is 1.5 ⁇ m.
• the lower cladding material 4 is undoped silica, with a refractive index n 4 of 1.446.
• the lower waveguide 1 and upper core 8 are fabricated following standard techniques. The last fabrication process is a deposition over the upper core 8 of the upper cladding 3, in particular by spin- coating, which is realized in DeSoliteTM 3471-1-129 produced by DSM.
• This polymer has a high thermo-optic coefficient equal to -2.6-10 "4 /°C so that a variation in temperature of 115 °C gives a change in the refractive index of 0.03.
• the grating period A is of 262 nm.
• Example 2 Fig. 4 shows an alternative embodiment of a contra-directional coupler 10.
• the lower input waveguide 1 is realized as in example 1, while the upper waveguide 2 is an inverse ridge waveguide having the upper cladding 3 in a tuneable material, particularly in made of SylgardTM.
• Upper core 8, lower core 7 and lower cladding 4 are made of silicon-compounds materials. This structure may be advantageous because an accurate control of the thickness of the core - and thus of the coupler birefringence - can be achieved. Indeed, to control the coupler birefringence, it is necessary to control, among others, the dimensions of the core.
• this can be obtained varying the size of the core, in the specific case the length of the side of its square cross-section, during the etching process. However during etching, an inaccuracy of about 3% in the dimensions is normally expected. On the other hand, controlling the thickness of a film, as in this case, is more accurate and therefore a more accurate control of the birefringence is obtained.
• the coupler of the present invention has a wide tuning range and at the same time is rather easy and relatively cheap to fabricate: fabrication is carried out using the desired materials optimised for the desired filter properties and the tuneable layer is applied only at the last stage as an upper cladding.
• the polymer is integrated with the standard and well tested materials without imposing any limitations in the other fabrication step and having at the same time a large tunability range guaranteed by this polymer cladding.
• Examples 1 and 2 are related to a contra-directional coupler, which is an easy device to fabricate and has a reliable response.
• a co-directional coupler can be obtained, which has a wider tunability despite of the more complex construction.
• Example 3 Figs. 5 and 6 schematically illustrate a cross-sectional view and a lateral cross- sectional view, respectively, of a co-directional coupler comprising two vertically stacked waveguides 1,2.
• the input waveguide is the lower waveguide 1 which has a Ge-doped silica square (6x6 ⁇ m 2 ) core 7 with refractive index n 6 of 1.456 and a silica cladding 4 with refractive index n 8 of 1.446 on a silicon wafer substrate 6.
• the square (6x6 ⁇ m 2 ) core 8 of the output waveguide 2 is realized in silicon oxynitride (SiO x N y ) and has a refractive index ns of 1.49.
• a metallic electrode 15 is placed on the top of the upper waveguide to actuate the tuning.
• the grating is realized on the top portion of the core of the output waveguide, in a location which is the most distant from the input waveguide to minimize transmission losses of the transmitted wavelengths.
• the bandwidth of this coupler is equal to 0.4 nm.
• An example of the spectra response of this coupler is given in Fig. 7, where the normalised power of the transmitted and of the dropped channel is shown.
• the resulting tuning range AX is of about 40 nm.
• the tuning range is relatively wide for the given temperature variation, compared to the contra- directional case.
• the grating couples the desired channel from the first waveguide to the other and also an undesired channel back to the input waveguide, giving rise to channel crosstalk if the wavelength of this back reflected signal belongs to the bandwidth of interest (to which the channels of the signal belong). Therefore, given a certain bandwidth, it is clear that if the refractive effective indices ni and n 2 are not sufficiently different (i.e. K is too small) then the grating wave-vector will not only couple light from one waveguide to the other at ⁇ 0 but may also
• a wave-vector diagram for the two waveguides is shown (it is imposed that n x > n 2 ). Explicitly shown are the amplitudes of the wave-vectors of the Bragg grating necessary for contra-directional coupling between the two
• the input waveguide ( K ).
• the C-band is considered as
• the grating K-vector should be made preferably larger than a certain number. It can be inferred from fig. 8 and eq. (I) that this condition is met when where ⁇ T min is the smallest allowed grating K-vector and ⁇ s the largest
• the grating assisted contra-directional coupler of the present invention will work correctly in the desired bandwidth, i.e. it will drop/add only at ⁇ 0 without affecting in any way any of the other wavelength
• a coupler 10 designed to work in the C-band
• the input waveguide is a
• the two waveguides are vertically stacked and
• the tuneable cladding is DeSoliteTM 3471-1-129 and the other cladding is undoped SiO 2 .
• a 1 cm-long grating is placed on the output waveguide. This coupler satisfies eq. (V) for the C-band and indeed the simulation plotted in fig. 10 shows a dropped channel at 1.556 nm.
• a second spurious channel reflected back into the input waveguide is present at 1.516 nm and it is well outside the desired bandwidth.
• Fig. 11 shows an add/drop optical device 100 according to the present invention.
• the add/drop device 100 comprises a plurality of couplers 10 in series so as to be able to drop more than one channel and/or to extend the available tuning range of the overall device.
• the coupler 10 has a tuning range of 7 nm (see for example the coupler of example 1), then six couplers of the same type in series will be able to drop any channel in a 42 nm bandwidth. In this case only a single coupler 10 will be active at a given time, the other couplers will be rendered inactive by tuning the coupler peak in between any two channels. If the coupler response is correctly designed (i.e. the bandwidth of the coupler should be smaller than Vi of the channel spacing and the sidelobe suppression should be of the order of 30 dB), then this will allow to effectively switch the coupler 10 on and off.

Landscapes

• Physics & Mathematics (AREA)
• Nonlinear Science (AREA)
• General Physics & Mathematics (AREA)
• Optics & Photonics (AREA)
• Optical Integrated Circuits (AREA)

Applications Claiming Priority (1)

Publications (1)

Family

ID=34610016

Family Applications (1)

Country Status (5)

Families Citing this family (15)

Citations (1)

Family Cites Families (8)

• 2003
  • 2003-11-05 EP EP03795805A patent/EP1680706A1/de not_active Withdrawn
  • 2003-11-05 WO PCT/EP2003/012328 patent/WO2005050306A1/en active Application Filing
  • 2003-11-05 CN CNA2003801106361A patent/CN1879056A/zh active Pending
  • 2003-11-05 AU AU2003298103A patent/AU2003298103A1/en not_active Abandoned
  • 2003-11-05 US US10/578,252 patent/US7292752B2/en not_active Expired - Fee Related

Patent Citations (1)

Non-Patent Citations (2)

Also Published As

Similar Documents

Legal Events